CU Vel needs to be very closely watched, as it has a normal outburst every 2-3 months, and a superoutburst about once a year. The next outburst is due any time. The last outburst appears to have been a superoutburst, based on observations made by Rod Stubbings (SRX, Tetoora Road, NSW, Australia) and submitted to the AAVSO International Database: 2012 October 15.646 UT, 11.1; 22.692, 15.3. No information is available to determine the start or end of the outburst more precisely. CU Vel is magnitude 17 V at minimum and can be as bright as 10.8 V at maximum (normal outburst or superoutburst; normal outbursts last only a few days).

Your observations are CRITICAL, as the HST planners will decide whether to observe CU Vel based on your observations. They will likely make this decision sometime on January 17.

As instructed in AAVSO Alert Notice 471, for CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. B filter would be best for a light curve, although for the magnitude estimates, a V measurement would be best. An uninterrupted light curve would be better than cycling between filters. At 17 V at minimum, CU Vel is most likely too faint for positive visual observations at minimum. If positive visual observations are possible, however, they are welcome, as are visual fainter-than observations fainter than magnitude 11.0.